The present invention relates generally to aircraft collision avoidance systems, and particularly, to predicting the presence of wake vortex turbulence of air traffic and displaying the information on a Traffic Alert and Collision Avoidance System, or TCAS.
Aircraft pilots are expected to visually identify collision threats and avoid them. This xe2x80x9csee and avoidxe2x80x9d technique based on the pilot""s visual sense remains the most basic method of aircraft collision avoidance. However, since the 1950""s electronic techniques based on radio frequency and optical transmissions have been developed to supplement the pilot""s visual sense. The government has developed and implemented a system of ground based and aircraft carried equipment designated the Air Traffic Control Radar Beacon System (ATCRBS). This system includes two different types of ground based radar emitters located at each of a plurality of Air Traffic Control (ATC) stations. One type of radar is referred to as the Primary Surveillance Radar (PSR), or simply as the primary radar. The primary radar operates by sending out microwave energy that is reflected back by the aircraft""s metallic surfaces. This reflected signal is received back at the ground radar site and displayed as location information for use by an air traffic controller. The second type of radar is referred to as the Secondary Surveillance Radar (SSR), or simply secondary radar. Unlike the primary radar, the SSR is a cooperative system in that it does not rely on reflected energy from the aircraft. Instead, the ground based SSR antenna transmits a coded 1030 MHz microwave interrogation signal. A transponder, i.e., a transmitter/receiver, carried on the aircraft receives and interprets the interrogation signal and transmits a 1090 MHz microwave reply signal back to the SSR ground site. This receive and reply capability greatly increases the surveillance range of the radar and enables an aircraft identification function, referred to as Mode-A, wherein the aircraft transponder includes an identification code as part of its reply signal. This identification code causes the aircraft""s image or blip on the ATC operator""s radar screen to stand out from the other targets for a short time. Thus, Mode-A provides an rudimentary identification function.
In addition to the identification function provided by Mode-A, the aircraft altimeter is typically coupled to the transponder such that a reply signal includes altitude information, referred to as Mode-C.
A ground based SSR sequentially transmits both Mode-A and Mode-C interrogation signals to aircraft in the area. Accordingly, the interrogation signal transmitted by the SSR contains three pulses. The second pulse is a side-lobe suppression signal transmitted from an omnidirectional antenna co-located with a mechanically rotating antenna which provides a highly directive antenna beam. The first and third pulses are transmitted by the directive antenna at a predetermined frequency and are separated by a predetermined interval. The time interval between the first and third pulses defines what information the interrogator is requesting: eight (8) microseconds for identification and twenty-one (21) microseconds for altitude. The operator of the ground based SSR sets the radar interrogation code to request either Mode-A or Mode-C replies from the aircraft transponder. Typically, the radar is set to request a sequence of two Mode-A replies followed by a single Mode-C reply. This sequence is repeated so that a radar operator continuously receives both the Mode-A identification code and the Mode-C altitude information. Upon receipt of the interrogation signal, the aircraft transponder develops and transmits a reply signal which includes the identification or altitude information. The ground based SSR receives and processes the transponder reply signal, together with time of arrival range information, to develop a measurement of position for each responding aircraft. Under such a system, the air traffic controller uses this information to involve the aircraft by radio, usually with voice communication, to maintain or restore safe separations between aircraft. The system is inherently limited because each aircraft needs be dealt with individually, which requires a share of the air traffic controller""s time and attention. When traffic is heavy, or visibility is low, collision potential increases.
During the 1960""s the increases in the number of aircraft, the percentage of aircraft equipped with transponders, and the number of ATCRBS radar installations began to overload the ATCRBS system. This system overload caused a significant amount of interference and garble in the Mode-A and Mode-C transmissions because of replies from many simultaneously interrogated aircraft. Furthermore, the Mode-A and Mode-C systems are unable to relay additional information or messages between the ground based SSR and the interrogated aircraft, other than the aforementioned identification and altitude information. The Mode Select, or Mode-S, was the response to this overload and other deficiencies in ATCRBS. Mode-S is a combined secondary surveillance radar and a ground-air-ground data link system which provides aircraft surveillance and communication necessary to support automated ATC in the dense air traffic environments of today.
Mode-S incorporates various techniques for substantially reducing transmission interference and provides active transmission of messages or additional information by the ground based SSR. The Mode-S sensor includes all the essential features of ATCRBS, and additionally includes individually timed and addressed interrogations to Mode-S transponders carried by aircraft. Additionally, the ground based rotating directive antenna is of monopulse design which improves position determination of ATCRBS target aircraft while reducing the number of required interrogations and responses, thereby improving the radio frequency (RF) interference environment. Mode-S is capable of common channel interoperation with the ATC beacon system. The Mode-S system uses the same frequencies for interrogations and replies as the ATCRBS. Furthermore, the waveforms, or modulation techniques, used in the Mode-S interrogation signal were chosen such that, with proper demodulation, the information content is detectable in the presence of overlaid ATCRBS signals and the modulation of the downlink or reply transmission from the transponder is pulse position modulation (PPM) which is inherently resistant to ATCRBS random pulses. Thus, the Mode-S system allows full surveillance in an integrated ATCRBS/Mode-S environment.
The Radio Technical Commission for Aeronautics (RTCA) has promulgated a specification for the Mode-S system, RTCA/DO-181A, MINIMUM OPERATIONAL PERFORMANCE STANDARDS FOR AIR TRAFFIC CONTROL RADAR BEACON SYSTEM/MODE SELECT (ATCRBS/MODE-S) AIRBORNE EQUIPMENT, issued January 1992, and incorporated herein by reference. According to RTCA specification DO-181, the airborne portion of the Mode-S system includes in one form or another at least a dedicated transponder, a cockpit mounted control panel, two dedicated antennas and cables interconnecting the other elements. As discussed more fully below, each aircraft may be within range of more than one SSR ground station at any time and must respond to interrogation signals broadcast from multiple directions. Therefore, the Mode-S system typically uses two single element omnidirectional antennas to receive interrogation signals from any quadrant and reply in kind.
In operation, a unique 24-bit address code, or identity tag, is assigned to each aircraft in a surveillance area by one of two techniques. One technique is a Mode-S xe2x80x9csquitterxe2x80x9d preformed by the airborne transponder. Once per second, the Mode-S transponder spontaneously and pseudo-randomly transmits, or xe2x80x9csquitters,xe2x80x9d an unsolicited broadcast, including a specific address code unique to the aircraft carrying the transponder, via first one and then the other of its antennas which produce an omnidirectional pattern. The transponder""s transmit and receive modes are mutually exclusive to avoid damage to the equipment. Whenever the Mode-S transponder is not broadcasting, it is monitoring, or xe2x80x9clistening,xe2x80x9d for transmissions simultaneously on its omnidirectional antennas. According to the second technique, each ground based Mode-S interrogator broadcasts an ATCRBS/Mode-S xe2x80x9cAll-Callxe2x80x9d interrogation signal which has a waveform that can be understood by both ATCRBS and Mode-S transponders. When an aircraft equipped with a standard ATCRBS transponder enters the airspace served by an ATC Mode-S interrogator, the transponder responds the with a standard ATCRBS reply format, while the transponder of a Mode-S equipped aircraft replies with a Mode-S format that includes a unique 24-bit address code, or identity tag. This address, together with the aircraft""s range and azimuth location, is entered into a file, commonly known as putting the aircraft on roll-call, and the aircraft is thereafter discretely addressed. The aircraft is tracked by the ATC interrogator throughout its assigned airspace and, during subsequent interrogations, the Mode-S transponder reports in its replies either its altitude or its ATCRBS 4096 code, depending upon the type of discrete interrogation received. As the Mode-S equipped aircraft moves from the airspace served by one ATC Mode-S interrogator into that airspace served by another Mode-S interrogator, the aircraft""s location information and discrete address code are passed on via landlines, else either the ground based SSR station picks up the Mode-S transponder""s xe2x80x9csquitterxe2x80x9d or the Mode-S transponder responds to the All-Call interrogation signal broadcast by the next ATC Mode-S interrogator.
The unique 24-bit address code, or identity tag, assigned to each aircraft is the primary difference between the Mode-S system and ATCRBS. The unique 24-bit address code allows a very large number of aircraft to operate in the air traffic control environment without an occurrence of redundant address codes. Parity check bits overlaid on the address code assure that a message is accepted only by the intended aircraft. Thus, interrogations are directed to a particular aircraft using this unique address code and the replies are unambiguously identified. The unique address coded into each interrogation and reply also permits inclusion of data link messages to and/or from a particular aircraft. To date, these data link messages are limited to coordination messages between TCAS equipped aircraft, as discussed below. In future, these data link messages are expected to include Aircraft Operational Command (AOC) information consisting of two to three pages of text data with flight arrival information, such as gates, passenger lists, meals on board, and similar information, as well as Flight Critical Data (FCD). However, the primary function of Mode-S is surveillance and the primary purpose of surveillance remains collision avoidance.
Collision avoidance systems which depend on aircraft carried transponders are usually divided into two classes: passive and active. The ATCRBS, including Mode-S, described above are passive systems because the transponder reply emissions alone provide the only information for locating and identifying potential threats. While passive systems tend to be simple and low cost when compared to active systems and do not crowd the spectrum with additional RF transmissions, detection of transponder emissions from other aircraft is difficult. A passive collision threat detector is essentially a receiver having sufficient intelligence to first detect and then locate the existence of potential collision threats represented by nearby aircraft. The aircraft""s receiver is of necessity operating in close proximity to the host aircraft""s ATCRBS transponder. Government regulations require the ATCRBS transponder to emit RF energy at 125-500 watts in response to interrogation signals from a ground based SSR. The transponder aboard any potential collision threat aircraft flying along a radial from the directional SSR antenna, usually about 3xc2x0 to 4xc2x0 wide, will respond at about the same time as the host aircraft""s transponder. The host aircraft""s transponder is so much closer, usually no more than a few feet, to any receiver that the host aircraft""s own response to the interrogation signal will swamp the response from any other aircraft in its vicinity. Thus, the host aircraft flies in a xe2x80x9cblindxe2x80x9d region wherein any potential threat aircraft is not xe2x80x9cseen,xe2x80x9d unless other provisions are made. This blind region expands as the target approaches the host. Furthermore, typically each aircraft is within range of more than one SSR site and a blind region is associated with each SSR site. Because wholly passive systems are generally believed insufficient for reliable collision avoidance, the government and aviation industry have cooperated in developing Operational Performance Standards for a Traffic Alert and Collision Avoidance System, known as TCAS, separate from the ATCRBS/Mode-S transponder system. The standards are set forth in the RTCA specifications DO-185, MINIMUM OPERATIONAL PERFORMANCE STANDARDS FOR AIR TRAFFIC ALERT AND COLLISION AVOIDANCE SYSTEM (TCAS) AIRBORNE EQUIPMENT, issued Sep. 23, 1983, consolidated Sep. 6, 1990, and DO-185A, MINIMUM OPERATIONAL PERFORMANCE STANDARDS FOR AIR TRAFFIC ALERT AND COLLISION AVOIDANCE SYSTEM II (TCAS II) AIRBORNE EQUIPMENT, issued December 1997, both of which are incorporated herein by reference.
FIG. 1 illustrates one known embodiment of the TCAS 1 having 4-element interferometer antennas 2A and 2B coupled to a radio frequency receiver 3 of a TCAS processor 4. Receiver 3 is coupled in turn to a signal processor 5 operating known traffic alert and collision avoidance software. A radio frequency transmitter 6 is coupled to signal processor 5 for broadcasting Mode-S interrogation signals. An associated control panel 7 for operating TCAS 1 and display 8 for displaying TCAS information are each coupled to signal processor 5 of TCAS processor 4, as described in each of U.S. Pat. No. 4,855,748 entitled, TCAS BEARING ESTIMATION RECEIVER USING A 4 ELEMENT ANTENNA, issued on Aug. 8, 1989, to Ruy L. Brandao et al and U.S. patent application Ser. No. 09/369,752 entitled, MULTIFUNCTIONAL AIRCRAFT TRANSPONDER, filed on Aug. 6, 1999, in the names of Daryal Kuntman, Ruy L. Brandao, and Ruy C. P. Brandao, the complete disclosures of which are incorporated herein by reference. TCAS is a well-known active collision avoidance system that relies upon reply signals from airborne transponders in response to interrogation signals from an aircraft equipped with an ATCRBS Mode-A/Mode-C or Mode-S transponder. The TCAS antenna is driven to produce a directional microwave transmission, or radiation, pattern carrying a transponder generated coded interrogation signal at 1030 MHz, the same frequency used by ground based SSR stations to interrogate Mode-S transponders. Whenever the TCAS transponder is not broadcasting, it is xe2x80x9clisteningxe2x80x9d for Mode-S xe2x80x9csquittersxe2x80x9d and reply transmissions at 1090 MHz, the same frequency used by Mode-S transponders to reply to interrogation signals. Thus, a TCAS equipped aircraft can xe2x80x9cseexe2x80x9d other aircraft carrying a transponder. Once a transponder equipped target has been xe2x80x9cseen,xe2x80x9d the target is tracked and the threat potential is determined by operation of known TCAS algorithms, as described in each of U.S. Pat. No. 5,077,673, AIRCRAFT TRAFFIC ALERT AND COLLISION AVOIDANCE DEVICE, issued Dec. 31, 1991, and U.S. Pat. No. 5,248,968, TCAS II PITCH GUIDANCE CONTROL. LAW AND DISPLAY SYMBOL, issued Sep. 28, 1993, the complete disclosures of which are incorporated herein by reference. Altitude information is essential in determining a target""s threat potential. As described in incorporated U.S. Pat. Nos. 5,077,673, and 5,248,968, comparison between the altitude information encoded in the reply transmission from the threat aircraft and the host aircraft""s altimeter is made in the TCAS processor and the pilot is directed obtain a safe altitude separation, by descending, ascending or maintaining current altitude.
Collision avoidance is enhanced by including range information during threat determination. The approximate range, or distance between the host aircraft and the target, is based on the strength of the received transponder signal in response to an interrogation signal from the host aircraft. Modem TCAS systems obtain more accurate range information by measuring the time lapse between transmission of the interrogation signal and reception of the reply signal, commonly known as xe2x80x9cturn around time.xe2x80x9d The time to closest approach as determined by the TCAS processor is the primary consideration in threat determination.
Knowledge of the direction, or bearing, of the target aircraft relative to the host aircraft""s heading greatly enhances a pilot""s ability to visually acquire the threat aircraft and provides a better spatial perspective of the threat aircraft relative to the host aircraft. The TCAS processor can display bearing information if it is available. Bearing information is also used by the TCAS processor to better determine threat potential presented by an intruder aircraft. Directional antennas are used in some TCAS systems for determining angle of arrival data which is converted into relative bearing to a threat aircraft by the TCAS processor. Several methods exist for determining angle of arrival data. One common arrangement uses a phase matched quadrapole antenna array with output signals being combined such that the phase difference between two output ports of the combining circuitry indicates the bearing of a received transponder signal. Another method for determining angle of arrival data includes a method based on signal phase, commonly known as phase interferometry. Still another commonly known method is based on signal amplitude. Attenuation of the received transponder signals by the airframe blocking the antenna from the transmitter is often overcome by locating a primary directional antenna on a top surface of the aircraft and a second antenna on a bottom surface of the aircraft. The second or bottom antenna is sometimes omnidirectional which reduces cost at the expense of reduced directional coverage. Other TCAS systems provide duplicate directional antennas top and bottom. U.S. Pat. No. 5,552,788, ANTENNA ARRANGEMENT AND AIRCRAFT COLLISION AVOIDANCE SYSTEM, issued Sep. 3, 1996, the complete disclosure of which is incorporated herein by reference, teaches an arrangement of four standard monopole antenna elements, for example, xc2xc wavelength transponder antennas, arranged on opposing surfaces of one axis of the aircraft at the extremes of two mutually orthogonal axes to avoid shadowing and provide directional information about the received reply signal. For example, two monopole antennas are preferably mounted on a longitudinal axis of the aircraft and two additional monopole antennas are preferably mounted on a lateral axis of the aircraft orthogonal to the longitudinal axis passing through the first two antennas. Directionality is determined by comparing the power levels of the received signals. Additionally, U.S. Pat. No. 5,552,788 teaches a TCAS system which can transmit transponder interrogation signals directionally using predetermined ones of the monopole antennas, thus eliminating dependence upon ground based radar systems for interrogating threat aircraft transponders.
Other antennas for directionally transmitting TCAS system transponder interrogation signals are also commercially available. For example, a TCAS system-compatible directional antenna is commercially available from Honeywell, Incorporated of Redmond, Wash., under the part number ANT 81A.
The ATCRBS/Mode-S surveillance system and the TCAS collision avoidance system are generally separate, the algorithms operated by the TCAS processor account for the data provided by the intruder aircraft to determine what evasive maneuver to recommend to the host aircraft""s pilot, i.e., whether to recommend that the pilot maintain current altitude, ascend or descend. The TCAS system also uses the inter-aircraft data link provided by the addressable Mode-S transponder to coordinate the recommended evasive maneuver with a TCAS equipped intruder aircraft. Furthermore, a connection between the TCAS and Mode-S transponders and other avionics on an aircraft allows coordination between the TCAS and Mode-S transponders.
The TCAS is also coupled to provide an output signal to one or more displays as described in above incorporated U.S. patent application Ser. No. 09/369,752. The function of the display is described in detail in connection with FIG. 2.
FIG. 2 shows one configuration of a conventional display 10 used with a TCAS collision avoidance system. Display 10 includes an aircraft symbol 12 to depict the position of the host aircraft. A circle, formed by multiple dots 14 surrounding host aircraft position symbol 12, indicates a 2 nautical mile range from the host aircraft. Generally, semi circular indicia 16 around the periphery of indicator display 10 and a rotatable pointer 18 together provide an indication of the rate of change of altitude of the host aircraft. Indicia 16 are typically marked in hundreds of feet per minute. The portion of indicia 16 above the inscriptions xe2x80x9c0xe2x80x9d and xe2x80x9c6xe2x80x9d indicates rate of ascent while the portion below indicates rate of descent.
Other target aircraft or xe2x80x9cintrudersxe2x80x9d are identified on display 10 by indicia or xe2x80x9ctagsxe2x80x9d 20, 22 and 24. Tags 20, 22, 24 are shaped as circles, diamonds or squares and are color coded (not shown) to provide additional information. Square 20 colored red represents an intruder entering warning zone and suggests an immediate threat to the host aircraft with prompt action being required to avoid the intruder. Circle 22 colored amber represents an intruder entering caution zone and suggests a moderate threat to the host aircraft recommending preparation for intruder avoidance. Diamond 24 represents near or xe2x80x9cproximate trafficxe2x80x9d when colored solid blue or white and represents more remote traffic or xe2x80x9cother trafficxe2x80x9d when represented as an open blue or white diamond. Air traffic represented by either solid or open diamond 24 is xe2x80x9con filexe2x80x9d and being tracked by the TCAS.
Each indicia or tag 20, 22, 24 is accompanied by a two digit number preceded by a plus or minus sign. In the illustration of FIG. 2 for example, a xe2x80x9c+05xe2x80x9d is adjacent circle tag 20, a xe2x80x9cxe2x88x9203xe2x80x9d is adjacent square tag 22 and a xe2x80x9cxe2x88x9212xe2x80x9d is adjacent diamond tag 24. Each tag may also have an vertical arrow pointing either up or down relative to the display. The two digit number represents the relative altitude difference between the host aircraft and the intruder aircraft, the plus and minus signs indicating whether the intruder is above or below the host aircraft. Additionally, the two digit number appears positioned above or below the associated tag to provide a visual cue as to the intruder aircraft""s relative position: the number positioned above the tag indicates that the intruder is above the host aircraft and the number positioned below the tag indicates that the intruder is below the host aircraft. The associated vertical arrow indicates the intruder aircraft""s altitude is changing at a rate in excess of 500 feet per minute in the direction the arrow is pointing. The absence of an arrow indicates that the intruder is not changing altitude at a rate greater than 500 feet per minute.
Display 10 includes several areas represented by rectangular boxes 26, 28, 30, 32, 34 which are areas reserved for word displays wherein conditions of the TCAS are reported to the pilot of the host aircraft. For example, if a portion or component of the TCAS fails, a concise textual report describing the failure appears in one of rectangular boxes 26, 28, 30, 32, 34. In another example, if the operator operates mode control 36 to select one of a limited number of operational modes, a concise textual message indicating the choice of operational mode appears in another of rectangular boxes 26, 28, 30, 32, 34. Selectable operational modes typically include a xe2x80x9cstandbyxe2x80x9d mode in which both of the host aircraft transponder systems are inactive, a xe2x80x9ctransponder onxe2x80x9d mode in which a selected one of primary transponder and secondary transponder is active, a xe2x80x9ctraffic alertxe2x80x9d mode in which an alert is transmitted to the host aircraft pilot if any Mode-C or Mode-S transponder equipped aircraft are entering a first predetermined cautionary envelope of airspace, and a xe2x80x9ctraffic alert/resolution advisoryxe2x80x9d mode in which a traffic alert (TA) and/or resolution advisory (RA) is issued if any Mode-C or Mode-S transponder equipped aircraft are entering a second predetermined warning envelope of airspace. The various operational modes described above are selectable by operating mode control 36.
The Vertical Speed Indicator (VSI) portion of indicator display 10, formed by the semi circular indicia 16 around the periphery and rotatable pointer 18, are used in the TCAS to indicate a rate of climb or descent that will maintain the safety of the host aircraft. In the particular example of FIG. 2, a colored arc portion 40, referenced by double cross-hatching, of the VSI scale indicates a recommended rate of climb intended to ensure the safety of the host aircraft. Another colored arc portion 42, referenced by single cross-hatching, of the VSI scale indicates a rate of descent which the TCAS recommends against for the host aircraft in the current situation. The operator of the intruder aircraft receives instructions coordinated with the host aircraft TCAS.
Present visual flight displays fail to include accurate information regarding on board detection and display of accurate wake vortex information of air traffic. Thus, aircrews are not currently shown the location nor intensity of wake vortices created by other planes. This lack of information represents a significant aviation hazard that could result in injuries to passengers and crew, or, potentially, damage and loss of the airplane. Wake vortex turbulence during landing approach poses commercial penalties as spacing requirement at airports have been adjusted farther than otherwise necessary. This increased spacing results in fewer landings for many operators. In other words, in the absence of better information, the FAA has leaned on the side of caution and imposed certain spacing rules which on average are more than is required for safe separation in the presence of wake vortex turbulence. Some operators must conduct extensive overhaul and inspection of aircraft, which have experienced uncommanded roll and pitch to insure that the aircraft equipment is not at fault. In many cases the cause is wake vortex turbulence. However, since operators cannot demonstrate that wake vortex turbulence is the cause they sometimes remove aircraft from operation for up to two days, thus incurring significant and potentially unnecessary financial penalty.
The pilots of modern aircraft have on-board radar systems capable of detecting large areas of turbulence such as windshear. This turbulence is usually depicted as radar lines or xe2x80x9cwavesxe2x80x9d to indicate that an area or turbulence has been detected. Wake vortices, however, are not currently detectable by on-board systems, with the exception of some experimental trials having very short detection and warning ranges, on the order of less than 30 seconds"" warning distance. Currently, no system exists for predicting and detecting this type of turbulence at longer ranges or to depict the location and/or intensity of another aircraft""s wake vortex in a manner such that the pilots can maneuver to avoid its dangerous effects.
Parallel approaches are another problem area which is not adequately addressed in the prior art. At present no method or device in known to the inventors that provides a visual display of other aircraft encroaching on the flight path of the host aircraft during simultaneous approach on parallel runways. Instrument Landing System (ILS), the system that provides lateral, along-course, and vertical guidance to aircraft attempting to land, is inadequate to the task of maintaining separation during landing because the displayed localizer signal on the ILS approach does not support independent parallel approaches. As shown in FIG. 3, the overlap 50, represented by cross-hatching, between localizer paths 52A and 52B to parallel runways 54A and 54B, respectively, shows that even strict adherence to the ILS signal by both pilots can result in intersecting flight paths. The problem is particularly acute at airports with closely spaced parallel runways. Although parallel approaches may be adequately staggered in fair weather and the ILS is intended to maintain an adequate vertical separation between aircraft until an approach is established, bad weather decreases airport capacity and compounds the problems of parallel approaches. For example, Mode-S Specific Protocol (MSP) arrival rates may double from 30 arrivals per to hour during fair weather to 60arrivals per hour during nominally cloudy conditions, in part because airlines schedule flights as if every day is fair weather.
NASA (Langley) modified the traffic alerting algorithms known as Airborne Information for Lateral Spacing (AILS) algorithms, which are incorporated herein by reference. The NASA modified AILS algorithms added a vertical dimension, modified protected zones from circles to ellipses for added safety, and changed to using actual states once the aircraft moves off intended path. Three alert types: 1) navigation performance (navigation alert); 2) host ship threat to adjacent ship (path alert); and 3) adjacent ship threat to host ship (traffic alert), and two alert levels: 1) Caution (yellow) for situational awareness; and 2) Warning (red) for performing an emergency escape maneuver, are used. However, to date no visual simulation has been available to pilots for quick and easy assessment of the traffic situation during parallel approaches.
As discussed in Amy R. Pritchett""s paper Pilot Situation Awareness And Alerting System Commands, copyright 1998 by Society of Automotive Engineers, Inc., the complete text of which is incorporated herein by reference, two commonly stated objectives of modern cockpit systems are improving pilot situation awareness and adding the safety benefits of sophisticated alerting and command generation functions. Pritchett""s paper concludes that expected gains in safety are not realized if these two functions appear to provide conflicting or dissonant information to the pilot.
The TCAS and Mode-S sensor and datalink technologies described above enable displays to provide information both internal and external to the aircraft. Such enhancements to pilot situation awareness are normally expected to provide the pilot with better situation awareness which should serve as a basis for more accurate decisions. However, TCAS is intended to fulfill an xe2x80x9cexecutivexe2x80x9d role wherein the system is provided with automatic means to assess hazards, evaluate if an alert is required to cue an action, and decide upon evasive maneuvers to prevent or resolve the hazardous condition with the implicit assumption that the pilot quickly and precisely executes the commands.
However, studies indicate that the pilot situation awareness and executive alerting systems are often perceived by pilots to provide conflicting or dissonant information with the result that pilots do not always automatically execute the evasive maneuver recommended by the TCAS. Rather, pilots actively evaluate the situation based on information available to them through traffic situation displays and other sources, such as visual acquisition and air traffic control communications, to independently determine avoidance maneuvers. Pritchett""s studies examined the effects of TCAS situation displays and automatic executive alerts on pilot reactions to potential collisions generally, and during parallel approaches particularly, and identified both a high rate of nonconformance to TCAS commands and an interaction between nonconformance and TCAS traffic situation displays.
Pritchett""s paper suggests that either the TCAS commands could become mandatory while any conflicting information is deleted from the display, or alternatively, the TCAS commands could provide pilots with higher levels of situation awareness, which increases pilots"" ability to understand and verify the alerting logic and encourages pilots to use better decision making strategies. Pritchett concludes that pilots may perceive that the TCAS may not include all relevant information in its decision making, which promotes a lack confidence in the TCAS and a felt need to evaluate the situation and reconcile their decisions with the TCAS commands. Furthermore, pilots"" evaluation of the TCAS commands can significantly and unexpectedly delays their reaction. Additionally, inconsistencies between pilots"" decisions and the TCAS commands may cause pilots to execute different than expected responses to the hazard. Increasing pilots"" ability to understand and verify the alerting system""s logic may increase pilots"" trust to the extent that pilots do not feel a need to confirm or ignore the TCAS commands.
Although studies such as the above incorporated Pritchett paper suggest the need to present pilots with highly processed information required for the desired solution algorithms, and to display the objective functions operated by the alerting system in considering this information to promote pilot conformance to the commands, no currently operating TCAS system provides such information. Furthermore, the air traffic industry in general needs such information as RSVM in general, and in particularly needs visual simulations of relevant TCAS information for flying parallel approaches, during in-trail climbs, and for minimizing risk from wake vortices. Parent application Ser. No. 09/489,664 (Attorney Docket No. 543-99-010) satisfies the need to display visual simulations of such relevant TCAS information.
TCAS represents one known system exist for predicting airborne collisions. Other predictive systems are also known. For example, U.S. Pat. No. 5,325,302, entitled GPS-BASED ANTI-COLLISION WARNING SYSTEM, issued to Izidon, et al on Jun. 28, 1994, the complete disclosure of which is incorporated herein by reference, describes a method for predicting a collision between two or more relatively moving aircraft, including determining a respective position in space for each one of the aircraft relative to a fixed frame of reference at a predetermined frequency to produce successive frames of positional data for each aircraft with a coupled memory for storing the successive positional data frames, computing a trajectory for each aircraft relative to the fixed frame of reference, and predicting whether two or more trajectories will intersect.
However, while TCAS and other ways to predict collisions are known, none predict intruder aircraft wake vortex information, such as intensity, location, elevation or drift. Nor do such known collision prediction systems predict the host aircraft colliding with an intruder""s wake vortex. Thus, what is needed is a method for predicting intruder wake vortex information relative to the host aircraft.
The present invention overcomes the limitations of the prior art by providing a method and device for predicting intruder wake vortex information relative to the host aircraft. Preferably, predicted intruder wake vortex information is displayed using an air traffic alert and collision avoidance system (TCAS) display. The method and circuit of the present invention provide synthesized information to pilots by directly presenting information required for higher levels of situation awareness and decision making criteria used by the alerting system to pilots, whereby pilots are able to understand the basis for automatic commands.
The method of the present invention is a method for predicting the intensity and location of a wake vortex relative to a host aircraft resulting from a proximate intruder aircraft. The method of the invention includes determining a location of an intruder aircraft relative to the host aircraft; and determining information describing the wake vortex formed by the intruder. Preferably, the method of determining the wake vortex description includes determining the intruder aircraft type and configuration and determining local atmospheric conditions.
According to one aspect of the invention, the local atmospheric information determined and used by the invention includes one or more of the wind speed, the wind direction, and the local air temperature.
According to another aspect of the invention, the determination of the configuration of the intruder aircraft includes determining the position and altitude of the intruder aircraft relative to a local airport runway. Preferably, determining the altitude of the intruder aircraft relative to the local airport runway includes determining the barometric altitude of the intruder aircraft and determining terrain elevation information corresponding to the intruder""s position. The intruder""s barometric altitude is determined, for example, by retrieving Mode-C information from the intruder. The intruder""s position relative to a local airport is determined, for example, by comparing the intruder""s absolute position with a stored database of airport information. Various methods are known for determining the intruder""s absolute position. These various known methods, some of which are described in detail herein as examples, are all contemplated by the invention and are intended to be contained within the scope of the claimed invention.
According to still another aspect of the invention, the wake vortex of the intruder aircraft is determined as a function of: the intruder aircraft type information, including weight class; the intruder""s elevation and configuration; and local atmospheric conditions. According to one method of the invention, the intruder aircraft type, configuration, and local atmospheric conditions are used to access a look-up table of wake vortex information. According to an alternative method of the invention, the information is used to operate a model of wake vortex information.
According to yet another aspect of the invention, the probable strength and/or location of the wake vortex are determined as a function the intruder aircraft type, configuration, and local atmospheric conditions. According to various aspects of the invention, the strength and location information are determined by using the intruder aircraft type and configuration along with local atmospheric conditions to access a look-up table of wake vortex information. According to an alternative method, the invention uses the information to operate a model of wake vortex information.
Preferably, the invention includes displaying the wake vortex information. The wake vortex information is displayed, for example, on the TCAS display using the visual symbology described herein.
According to one aspect of the invention, the trajectory or flight path of the host aircraft is compared to the predictions of the wake vortex to determine whether continuation on the present flight path will cause the host aircraft to intersect or collide with the intruder""s wake vortex. Preferably, the invention generates an alert if an intersection or collision is predicted. The alert is any of a visual and/or aural alert. A visual alert is preferably displayed on the TCAS display. An aural alert is generated in meaningful and unambiguous terms.
According to still another aspect of the invention, the wake vortex information is recorded, for example, using a nonvolatile memory coupled to the circuit operating the algorithm of the invention.
The method of the present invention includes configuring a TCAS display of a host aircraft to display an icon representing another aircraft within a predetermined range; delineate the icon; and display a visual symbol describing a relative velocity of the other aircraft.
According to one aspect of the invention, delineating the icon includes delineating one of one or more icons representing different aircraft within the predetermined range in response to a selection input by the operator or pilot. The method of delineating the icon includes any of forming a wireline-type delineator around the selected icon, flashing or xe2x80x9cblinkingxe2x80x9d the selected icon alternately on and off; changing the color of the selected icon, and changing the shape of the selected icon.
According to another aspect of the invention, the method of displaying a visual symbol describing a relative velocity of the other aircraft includes displaying a visual symbol indicative of a relative velocity having a value greater than a predetermined threshold value. Furthermore, the method includes displaying a relative heading of the other aircraft and a different visual symbol indicative of a relative velocity having a value less than said predetermined threshold value.
According to other aspects of the invention, the invention includes displaying a visual symbol descriptive of the wake vortex created by the other aircraft. This visual symbol also preferably indicates the orientation of the wake vortex by any of aligning the visual symbol with the relative heading of the other aircraft, aligning the visual symbol with an average position of the wake vortex, and aligning the visual symbol with the path of the wake vortex.
According to other aspects of the invention, the invention includes displaying a visual symbol describing the intensity of the wake vortex, or alternatively, describing the intensity of the wake vortex in combination with information describing the orientation of the wake vortex. The visual symbol describing the intensity of the wake vortex describes either the speed of the other aircraft, or the geographic length of the wake vortex.
According to still another aspect of the invention, the invention includes displaying a textual message including flight identification of the other aircraft.
According to yet another aspect of the invention, the invention includes displaying a visual symbol defining a zone of xe2x80x9cprotectedxe2x80x9d airspace between the host aircraft and the icon-represented aircraft during a parallel approach. Preferably, the invention identifies a probable incursion of the protected airspace which will occur within a predetermined time period. Furthermore, the invention also preferably displays a visual symbol identifying an actual incursion of the protected airspace.
According to still other aspects of the invention, the invention provides an advanced TCAS display embodying one or more of the methods of the invention.